Continuous constant pressure process for staging solid-vapor compounds

ABSTRACT

An improved apparatus for staging solid-vapor complex compounds comprises heat exchange means for transferring heat from super-heated refrigerant vapor from a desorbing reactor to cooled refrigerant vapor directed to an adsorbing reactor. In another embodiment a liquid subcooler is used to cool liquid refrigerant passing from a condenser to an evaporator with cold refrigerant gas directed to an adsorbing reactor from the evaporator.

This application is a divisional of application Ser. No. 07/716,065,filed Jun. 17, 1991 now U.S. Pat. No. 5,241,831, which is acontinuation-in-part of co-pending application Ser. No. 07/436,431 filedNov. 14, 1989 now U.S. Pat. No. 5,025,635.

BACKGROUND OF THE INVENTION

In the aforesaid-application there are described apparatus and methodsfor staging sold-vapor compounds, the descriptions of which areincorporated herein by reference.

The use of compounds comprising solid-vapor compositions formed byadsorption, sometimes referred to as absorption, of gas molecules on asolid adsorbent as heat pump working materials is known in the art. Heatpump systems using such materials have a number of advantages over otherheat pumps for residential and commercial space conditioning, industrialheat pumping and refrigeration. Such advantages include highertemperature lift created by the solid-vapor media as compared to othersorption media thus eliminating the need for cooling towers or liftstaging. Moreover, the apparatus used for the solid-vapor compound heatpumps require few, if any, moving parts, resulting in simple andreliable hardware. Additionally, such systems do not use theobjectionable CFC's.

The solid-vapor compounds suitable for heat pumps include complexcompounds which are materials which adsorb molecules of gas to formcoordinative bonds in which the gaseous reactant coordinates viaelectron displacement with the solid adsorbent, commonly a solid metalinorganic salt. The adsorption/desorption process releases significantheat during adsorption and adsorbs energy during the desorption phase.Unlike most other sorption processes, the entire adsorption ordesorption reactions may occur at constant temperature thus eliminatingproblems with hot and cold sorber ends. Useful gaseous reactants includewater, ammonia, methanol, methane, ethane and the like. A number of suchmaterials are described in U.S. Pat. Nos. 4,822,391 and 4,848,944. Suchcompounds and their uses described in the aforesaid patents areincorporated herein by reference.

Heat activated heat pumps consist of a heat engine subsystem whichgenerates high pressure refrigerant vapor, essentially a thermalcompressor, and a heat pump subsystem which uses high pressurerefrigerant to produce cooling or heat pumping. The thermal compressor,heat pump, and their combination in a heat activated heat pump compriseuseful thermodynamic systems which make advantageous use of solid-gasreactions. In the aforesaid application there are described apparatusand methods using continuous constant pressure staging techniquesresulting in improved heat activated heat pump systems. It is an objectof the present invention to use such reactions and staging techniques toeven greater advantage and efficiency.

SUMMARY OF THE INVENTION

In the present invention, there are provided apparatus improvements usedin the heat activated heat pump described in the aforesaid co-pendingapplication. These improvements include a vapor recuperator and a liquidsubcooler, may be used individually, or in combination. The vaporrecuperator is used with a system incorporating a refrigerant condenserand evaporator, or absorber/desorber receivers for gaseous reactantdirected to and from the reactors. The liquid subcooler is used only ina refrigerant phase change (condenser/evaporator) system. In anotherembodiment, multiple-circuits for directing different heat transferfluids through the reactors are-disclosed. In yet another embodiment,preferred reactant media comprise the use of one or more specificcomplex compounds in the set or plurality of compounds in the differentreactors. These preferred complex compounds are disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are schematic illustrations of an apparatus of theinvention incorporating a vapor recuperator;

FIG. 3 is a schematic illustration of an apparatus of the inventionincorporating a liquid subcooler;

FIG. 4 is a schematic illustration of the same apparatus on theinvention incorporating both a vapor recuperator and subcooler; and

FIG. 5 illustrates a mechanically activated heat pump apparatusembodiment.

DETAILED DESCRIPTION Heat Activated Heat Pump

As used herein, the term "compound" is intended to mean any reactionproduct formed by adsorption and desorption, i.e. chemisorption, of agaseous reactant on a solid reactant within the scope of the invention.In practicing the continuous staging of a constant pressure engine cycleaccording to the invention, a plurality of two or more different solidreactants are selected, and a plurality or set of different solidreactants is introduced into each reactor in the heat pump apparatus.Each of the compounds of such sets or groups each exhibit differentvapor pressure curves, i.e. each has a different vaporpressure-temperature relationship, and which is independent of theconcentration of the gaseous reactant. Thus, each of the compounds in aset in a reactor adsorb and desorb the same gaseous reactant at adifferent temperature at the reaction pressure in the reactor. Compoundsare selected and arranged in the reactor in sequence of ascending orderof gas vapor pressure. Preferably the compounds of the series areselected so that none of the compounds in the same reactor have anadditional coordination step at lower equilibrium temperature which mayadsorb more reactant gas from the other compounds during temperatureequilibrium or shut-down condition which would reduce cycle performanceduring intermittent operation. Moreover, masses of each compound areadjusted so that the amount of heat required to desorb each-compound isrelated to the temperature difference between that compound and the nexthigher temperature compound.

The compounds are arranged in the reactors in sequence based on thecompound gaseous vapor pressure, and preferably are arrangedsuccessively in ascending order of gas vapor pressure. The reactors areprovided with means for directing a heat transfer fluid to thermallycommunicate with the compounds. During process operation the heattransfer fluid is gradually cooled as it passes through a desorbingreactor in which the successive compounds desorb the gaseous reactant atsuccessively lower temperatures. In the adsorbing reactor, the fluidwill become gradually heated as it is successively exposed thermally tothe succession of adsorbing compounds in which next successive compoundin the sequence adsorbs at a higher temperature.

Specific reactants used to form compounds useful in the inventioninclude metal oxides, halide, carbonates, nitrites, nitrates, oxalates,sulfides and sulfates. Preferred metals for the inorganic salts areselected from alkali and alkaline earth metals, transition metals,aluminum, zinc, cadmium and tin. Preferred transition metals aremanganese, iron, nickel, and cobalt. Hereinafter these reactants will besometimes referred to as solids, salts or solid reactants.

Gaseous reactants which are adsorbed on the solids to form compoundswhich are especially useful in the processes of the invention areammonia, water, methylamine and methanol, ammonia being especiallysuitable because it is stable, and forms high energy complexes. However,sulfur dioxide, other lower alkanols, lower alkanes, particularlymethane and ethane, pyridine, alkylamines, polyamines and phosphine mayalso be used as may carbon dioxide with metal oxides. These gaseousreactants may also be referred to as refrigerants herein. Particularlypreferred systems incorporate a set or series of ammoniated complexcompounds which include one or more of the following:

Ba Cl₂ •0-8 (NH₃), Sr Cl₂ •1-8 (NH₃), Sr Br₂ •2-8 (NH₃),

Ca Cl₂ •0-1 (NH₃), Ca Cl₂ •1-2 (NH₃), Ca Cl₂ •2-4 (NH₃),

Ca Cl₂ •4-8 (NH₃), Ca Br₂ •2-6 (NH₃), Ni Cl₂ •2-6 (NH₃),

Fe Cl₂ •2-6 (NH₃), Fe Br₂ •2-6 (NH₃),

Co Cl₂ •2-6 (NH₃), Co Br₂ •2-6 (NH₃),

Mg Cl₂ •2-6 (NH₃), Mg Br₂ •2-6 (NH₃),

Mn Cl₂ •2-6 (NH₃), Mn Br₂ •2-6 (NH₃),

Cu SO₄ •2-5 (NH₃), Zn Cl₂ •1-4 (NH₃), and

Na BF₄ •0.5-2.5 (NH₃).

Although in the aforesaid complex compounds, numerical value of moles ofammonia per mole of salt is given, in some complexes, the mole rangegiven comprises several coordination steps. Thus, for example, in thecase of the Cu SO₄, Zn Cl₂ and particularly Na BF₄, a number ofdifferent reaction steps occur between the numerical limits given.Typically however, practical considerations only allow for use of aportion of the designed coordination range. Accordingly, the aforesaidranges are intended to be approximate as will be understood by thoseskilled in the art.

In a specific example of a set or series of compounds, to illustrate asystem according to the invention, salts MgBr₂, CoBr₂, CoCl₂, CaBr₂ andSrBr₂ are used in a heat pump consisting of two separate reactionvessels. The compounds comprise the ammonia ligand complex compound ofthe aforesaid salts with the MgBr₂, CoBr₂, CoCl₂ and CaBr₂ salts formingcomplexes containing 2 to 6 NH₃ and SrBr₂ containing 2 to 8 NH₃. FIG. 1illustrates schematically an example of an apparatus embodiment forcarrying out the continuous constant pressure staged heat pump with thecompounds designated A-E respectively in the order given above beginningwith MgBr2•x (NH₃). The salts are charged to reactors 10 and 20, insuccessive ascending order of the complex compound ligand vaporpressure. Thus, the set of salts in each reactor is aligned as shownsuccessively A-E. In each reactor, there is provided a conduit orequivalent means for supplying a heat transfer fluid to thermallycontact the compounds. The compounds may be present in a column in theorder as shown, with the transfer fluid supply means comprising a pipeand having suitable means for example, fins to exchange heat with thecompounds. The apparatus includes a burner or furnace 15 with conduits26, 28, 38 and 42 which direct the heat transfer fluid between furnace15, reactors 10 and 20, and heat exchanger 25. A valve 22 and pump 18provide means to assist in directing the heat transfer fluid through thesystem. Evaporator 30 and condenser 32 are also connected with thereactors via pipes 36, 37, 38 and 39 and valve 35 for directing ammoniavapor to the condenser from the reactors and from the evaporator to thereactors. Valve 35 may also comprise a pair of check valves.

In a first reaction phase or half-cycle, valve 22 is positioned suchthat hot heat transfer fluid is directed via conduit 26 and into reactor10. With the compounds arranged according to their ascending order ofvapor pressure the heat transfer fluid will successively thermallycommunicate with the compounds in the set as it travels along the lengthof reactor 10.

In this reaction cycle, reactor 10 is the desorption reactor whilereactor 20 is the adsorption reactor. Reactor 10 is pressurized to afirst pressure, while reactor 20 is pressurized to a second pressure,lower than the first pressure. The desorption reactions in reactor 10are driven by the heated heat transfer fluid introduced into the reactorvia pipe 26 thereby driving these desorption reactions, successively,whereby the heat transfer fluid is gradually cooled as it gives up heatto the desorbing compounds. The cooled heat transfer fluid is thendirected via conduit 28 through heat exchanger 25 where it is furthercooled to a temperature suitable for introduction into reactor 20 viaconduit 29. Reactor 20, in this phase or half-cycle of the process, isthe adsorbing reactor in which the set of compounds therein adsorb thegaseous reactant in exothermic reactions. In this reactor, the heattransfer fluid is gradually heated as it is directed along the reactorand is successively exposed thermally to the exothermic adsorptionreactions at successively higher temperatures. Thus, as the heattransfer fluid leaves reactor 20 via pipe 42, it is heated substantiallyrelative to the temperature at which it was introduced via pipe 29. Theheat transfer fluid is then directed back to furnace 15 where it isagain heated to the temperature necessary for driving the endothermicreactions in reactor 10.

During this cycle of the process, the gaseous reactant from thedesorption reactor 10 is directed to the condenser 32, and gaseousreactant for the adsorption reactions in reactor 20 is obtained fromevaporator 30. The evaporator and condenser are in thermal contact withheat exchangers, not shown for transferring and recovering energy to andfrom the gaseous reactant.

In the second half-cycle or phase of the process, the pressure in thereactors is reversed such that reactor 20 becomes the desorbing reactorwith reactor 10 being the adsorption reactor. Valve 22 is adjusted sothat the heated heat transfer fluid is directed initially via pipe 42 toreactor 20, with the reactions then occurring as previously described inthe first reaction phase but with the reactors reversed for adsorptionand desorption. At the conclusion of the second half-cycle, the valvesare again reversed and the first half-cycle as above described repeated.

The specific example of the aforesaid set of ammoniated complexcompounds and typical adsorption and desorption reaction temperaturesand pressures are further illustrated and described in the aforesaidincorporated copending application. Although the apparatus illustratedshows only two reactors, it is understood that a plurality of two ormore reactors may be used, and hereinafter the term reactor orreactor(s) is intended to include one or a plurality of reactors. Theaforesaid specific complex compounds may be used in a heat activatedheat pump system incorporating an evaporator and condenser in which thegaseous reactant goes through a gas/liquid phase change, or used in asystem in which reactors for adsorbing (absorbing) and desorbing thegaseous reactant replace the evaporator and condenser, as disclosed inthe aforesaid copending application and incorporated herein byreference. These specific and preferred complex compounds may also beused in mechanical or pressure driven heat pump systems as alsodescribed and illustrated in the aforesaid copending application whichdescription is also incorporated herein by reference. Such an apparatusis illustrated in FIG. 5, in which a compressor 40 is used for providinghigh-pressure refrigerant vapor to the reactors in cooperation with theconduits to and from the reactors and valve 34 for directing the gaseousreactant to and from the reactors. Heat exchangers 25 and 27 are used toremove or introduce heat or energy to and from the heat transfer fluidpassing successively between the reactors. The compounds are introducedin a set of compounds in ascending order of complex compound vaporpressure.

VAPOR RECUPERATOR

According to the invention, an increase in the coefficient ofperformance (COP) and specific refrigeration capacity is provided by avapor recuperator, comprising a heat exchanger located along the flowpaths of the gaseous reactant to and from the reactor(s). As illustratedin FIG. 1, the vapor recuperator 40 is placed conveniently along theconduits 38 and 39 between reactors 10 and 20 and the evaporator 30 andcondenser 32, respectively. At such a location, the recuperator 40provides for heat exchange between the gaseous reactant vapor streamsflowing between the reactor(s) and the condenser, and between theevaporator and the reactor(s). The recuperator may be located on eitherside of the valve 35, although where check valves are used, the positionillustrated is preferred. By incorporating such a recuperator,super-heated vapor flowing from the desorption reactor(s) toward thecondenser is cooled against the relatively cool vapor directed from theevaporator to the adsorption reactor(s). Because energy recuperated fromthe superheated refrigerant leaving the desorption reaction istransferred to the cold gaseous refrigerant typically leaving theevaporator and then undergoing exothermic adsorption, thermal efficiencyof the system is increased.

In the embodiment shown in FIG. 2, reactors 12 and 14 are substitutedfor the evaporator and condenser components used in the refrigerantphase charge apparatus of FIG. 1. Such reactors, contain a solid orliquid salts for alternately adsorbing (absorbing) and desorbing thegaseous reactant directed thereto from the staging reactors 10 and 20.The reactors 12 and 14 cooperate with heat exchanges for recovery ofenergy from the alternating chemisorption reaction as described in theaforesaid application and incorporated herein by reference. The vaporrecuperator 40 functions the same way in this embodiment as in FIG. 1,to cool super-heated refrigerant vapor directed from a staging desorbingreactor (10 and 20) to an adsorbing reactor (12 or 14), against therelatively cool vapor directed from a desorbing reactor (12 or 14) to astaging adsorbing reactor (10 or 20).

LIQUID SUBCOOLER

In another embodiment of the invention, a liquid subcooler is used in arefrigerant phase change apparatus incorporating an evaporator andcondenser. As illustrated in FIG. 3, a liquid subcooler 42 comprising aliquid-vapor heat exchanger is provided for cooling liquid gaseousreactant flowing from the condenser to expansion valve 31 via conduit 33against relatively cold vapor of the gaseous reactant exiting theevaporator 30. The liquid subcooler 42 is conveniently located along theconduits 33 between the condenser 32 and evaporator 30 on the condenserside of expansion valve 31, or other gas expansion means, and conduit38, whereby these fluid streams are in thermal communication to providefor heat may be transfer therebetween. This heat transfer causes theliquid gaseous reactant in conduit 33 to become subcooled by the heatexchange against the relatively cold vapor from the evaporator inconduit 38 whereby a smaller fraction of the liquid will flash to vaporin isenthalpic expansion thereby increasing the cooling efficiency andcapacity of the system based on the amount of refrigerant fluid directedthrough the system. A further advantage of the subcooler is increasingthe energy provided in the vapor stream from the evaporator to theadsorbing reactor thereby ultimately decreasing the amount of primeenergy needed to drive desorption reactions. Accordingly, refrigerationcapacity and COP are both increased.

In FIG. 4, an example of an apparatus incorporating both the vaporrecuperator 40 and liquid subcooler 42 is illustrated.

FIG. 4 also illustrates an embodiment using multiple-circuits fordirecting heat transfer fluids to and from the salts in the reactorswith the heat transfer fluids passing through the reactors isillustrated. For each of the reactors 10 and 20 there are illustratedtwo heat transfer circuits, conduits 19 and 26 for directing fluids to,from and through reactor 10, and circuits 17 and 42 for reactor 20. Theuse of multiple circuits in the reactors provides for the use ofdifferent heat transfer fluids and different phases of those fluids. Forexample, a reactor might be direct fired with flue gas or exhaust fromfurnace 15 during the desorption phase, and a different fluid or otherheat transfer liquid used for rejecting or removing the heat during theadsorption phase. Although only two circuits are illustrated, the numberof circuits is not to be limited. A plurality of different heat transferfluids may be used in different circuits to maintain heat transfer overthe temperature of the heat exchange required in the staging of thereactors and compounds. The use of specific and different heat transferfluids may be tailored to the system, depending on a differentcombination of salts and the temperature ranges achieved in the reactionphases. The heat transfer fluids may be chosen to take optimum advantageof their respective heat transfer properties when used in such systems.Such multiple circuits may also be used to take advantage of using hightemperature exhaust gases from furnace 15 or from outside waste orreject heat sources by directing such heated fluids through thereactors. These as well as other advantages within the scope of theinvention will be evident to those skilled in the art.

We claim:
 1. An improved method of operating a mechanical or pressuredriven heat pump comprising:(a) selecting a plurality of two or moredifferent compounds comprising a solid reactant absorbent and a gaseousreactant absorbed thereon, wherein each of said compounds has adifferent gaseous reactant vapor pressure, substantially independent ofthe concentration of the gaseous reactant and wherein at least one ofsaid compounds is selected from the following:Ba Cl₂ •0-8 (NH₃), Sr Cl₂•1-8 (NH₃), Sr Br₂ •2-8 (NH₃), Ca Cl₂ •0-1 (NH₃), Ca Cl₂ •1-2 (NH₃), CaCl₂ •2-4 (NH₃), Ca Cl₂ •4-8 (NH₃), Ca Br₂ •2-6 (NH₃), Ni Cl₂ •2-6 (NH₃),Fe Cl₂ •2-6 (NH₃), Fe Br₂ •2-6 (NH₃), Co Cl₂ •2-6 (NH₃), Co Br₂ •2-6(NH₃), Mg Cl₂ •2-6 (NH₃), Mg Br₂ •2-6 (NH₃), Mn Cl₂ •2-6 (NH₃), Mn Br₂•2-6 (NH₃), Cu SO₄ •2-5 (NH₃), Zn Cl₂ •1-4 (NH₃), or Na BF₄ •0.5-2.5(NH₃), (b) locating a first set of the said different compounds in afirst reactor and a second set of the said different compounds in asecond reactor, wherein the compounds of each of said first and secondsets are located in said first and second reactors in successiveascending order of compound vapor pressure, (c) in a first reactioncycle, pressurizing said first reactor at a first pressure with saidgaseous reactant and said second reactor at a second pressure with saidgaseous reactant, higher than said first pressure, supplying a heattransfer fluid at a first temperature along said first reactor inthermal communication with said first set of compounds, whereby saidcompounds desorb said gaseous reactant in endothermic reactions,supplying a heat transfer fluid at a second temperature, higher thansaid first temperature, along said second reactor in thermalcommunication with said second set of compounds, whereby said compoundsabsorb said gaseous reactant in exothermic reactions, and (d) in asecond reaction cycle, pressurizing said second reactor at said firstpressure with said gaseous reactant and said first reactor at saidsecond pressure with said gaseous reactant, supplying heat transferfluid at a first temperature along said second reactor in thermalcommunication with said second set of compounds, whereby said compoundsdesorb said gaseous reactant in endothermic reactions, and supplyingheat transfer fluid at a second temperature, along said first reactor inthermal communication with said first set of compounds, whereby saidcompounds absorb said gaseous reactant in exothermic reactions, and (e)wherein desorbed and absorbed gaseous reactant is directed to and from amechanical or pressure driven compressor, respectively.
 2. The method ofclaim 1 wherein each of said compounds of said first set and each ofsaid compounds of said second set absorb and desorb the same gaseousreactant at a temperature different from the other compounds of each ofsaid sets, respectively, at the reaction pressures.
 3. The method ofclaim 1 including directing said heat transfer fluid through said firstand second reactors, respectively, in successive thermal communicationswith said successive compounds therein.